-elim (IHV W) -IHV #H1VW #H1WV
-elim (IHT U) -IHT #H1TU #H1UT
-@cpys_bind /2 width=1 by/ -HVW -H1VW -H1WV
-[ @(lsuby_cpys_trans … (L2.ⓑ{I}V))
-| @(lsuby_cpys_trans … (L1.ⓑ{I}V))
-] /4 width=5 by lsuby_cpys_trans, lsuby_succ/ (**) (* full auto too slow *)